When an image obtained by a digital camera or the like is printed, image processing such as lightness conversion processing, gradation conversion processing, white balance adjustment processing, color conversion processing, and sharpness processing is carried out thereon. The image after the image processing is then printed to obtain a print of a desired image quality. However, in conventional image processing, only one kind of parameter can be specified in each type of processing. Therefore, printing needs to be carried out repeatedly while changing a parameter in a trial and error manner until a print of a desired image quality can be obtained.
For this reason, a system has been proposed in Japanese Unexamined Patent Publication No. 11(1999)-136528 for letting a user select a desired one of images from a catalog image. In this system, processed images are obtained through image processing on the same image with use of various kinds of parameters whose values are set differently, and a catalog image is generated that includes the processed images. According to this system, a trial and error process is not necessary, and an image of a desired image quality can be obtained efficiently.
In the case where a parameter of lightness has been changed in image processing, the change in the parameter does not necessarily agree with a change of lightness perceived by human vision. For example, in the case where the value of the parameter of lightness has been doubled, the lightness of an image before and after the change does not seem to be doubled to human vision.
In the system described in Japanese Unexamined Patent Publication No. 11(1999)-136528, a range of change in each of the parameters is predetermined. Therefore, although parameters of various kinds are used for lightness, a degree of change in each of the parameters is predetermined. Consequently, the change does not agree with the change in lightness perceived by human vision, and a trial and error process still needs to be carried out until an image having lightness satisfying a user can be obtained.
The present invention has been conceived based on consideration of the above circumstances. An object of the present invention is therefore to generate a catalog of images whose lightness has been changed to become appropriate for perception by human vision.